Positive Ion Beam Research Articles

Extraction and neutralization of positive and negative ions from a pulsed electronegative inductively coupled plasma

Almost electron-free (ion-ion) plasmas can be transiently formed during the afterglow phase of pulsed plasmas in electronegative gases. In ion-ion plasmas, both positive and negative ions can be extracted which makes them advantageous for a number of applications. In this paper, we investigate the extraction and acceleration of positive and negative ion beams from a pulsed inductively coupled plasma in SF6. The plasma is bounded by two electrodes biased synchronously with the discharge modulation. It is shown that when a DC bias voltage is applied during the afterglow phase, positive/negative ions are accelerated in a positive/negative space charge sheath formed in front of one of the electrodes. The energy of extracted ions closely follows the amplitude of the applied bias voltage (25–150 V) and the peak beam current density reaches 2 A m−2. With a view to using the described system as a source of energetic neutral beams for low damage material processing, simultaneous extraction and surface neutralization of positive and negative ions using an extraction electrode with high aspect ratio apertures is investigated.

A space charge compensation model for positive DC ion beams

In this paper, we revisit and extend a formula to predict the compensation of space charge in positive DC ion beams of non-relativistic energy, as they are for example found in the injector beam lines of heavy ion accelerator facilities.The original formula was presented in 1975 by Igor Gabovich et al. and takes into account the de-compensation through Coulomb collisions of the primary beam ions and the compensating electrons. We extend its usability to arbitrary (positive) charge states of the ions and non-quasineutral beams.The resulting formula compares well with measurements using a retarding field analyzer and a multi-species generalization of it was incorporated into beam transport simulations using the particle-in-cell code WARP.

Ion field-evaporation from ionic liquids infusing carbon xerogel microtips

Ionic liquid ion sources capable of producing positive and negative molecular ion beams from room-temperature molten salts have applications in diverse fields, from materials science to space propulsion. The electrostatic stressing of these ionic liquids places the liquid surfaces in a delicate balance that could yield unwanted droplet emission when not properly controlled. Micro-tip emitter configurations are required to guarantee that these sources will operate in a pure ionic regime with no additional droplets. Porous carbon based on resorcinol-formaldehyde xerogels is introduced as an emitter substrate. It is demonstrated that this material can be shaped to the required micron-sized geometry and has appropriate transport properties to favor pure ionic emission. Time-of-flight mass spectrometry is used to verify that charged particle beams contain solvated ions exclusively.

Alternate extraction and acceleration of positive and negative ions from a gridded plasma source

By applying a square-wave voltage with frequencies between 10 kHz to 1 MHz to a set of grids terminating an ion–ion plasma source, we experimentally demonstrate the alternate extraction and acceleration of high energy (hundreds of eV) positive and negative ion beams. In addition, the ratio of positive-to-negative ion beam current can be controlled by adjusting the applied square-wave duty cycle. Temporally resolved floating potential measurements of a target show that the downstream potential can be controlled and sufficiently reduced at high applied frequencies (∼200 kHz), indicating that space-charge compensation can be achieved to prevent beam stalling.

Modulation instability and dissipative rogue waves in ion-beam plasma: Roles of ionization, recombination, and electron attachment

The amplitude modulation of ion-acoustic waves is investigated in an unmagnetized plasma containing positive ions, negative ions, and electrons obeying a kappa-type distribution that is penetrated by a positive ion beam. By considering dissipative mechanisms, including ionization, negative-positive ion recombination, and electron attachment, we introduce a comprehensive model for the plasma with the effects of sources and sinks. Via reductive perturbation theory, the modified nonlinear Schrödinger equation with a dissipative term is derived to govern the dynamics of the modulated waves. The effect of the plasma parameters on the modulation instability criterion for the modified nonlinear Schrödinger equation is numerically investigated in detail. Within the unstable region, first- and second-order dissipative ion-acoustic rogue waves are present. The effect of the plasma parameters on the characteristics of the dissipative rogue waves is also discussed.

Surface modification using ionic liquid ion beams

We developed an ionic liquid (IL) ion source using 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6) and produced IL ion beams by applying a high electric field between the tip and the extractor. Time-of-flight measurements showed that small cluster and fragment ions were contained in the positive and negative ion beams. The positive and negative cluster ions were deposited on Si(100) substrates. X-ray photoelectron spectroscopy measurements showed that the composition of the deposited layers was similar to that of an IL solvent. This suggests that a cation (A+) or an anion (B−) was attached to an IL cluster (AB)n, resulting in the formation of positive cluster ions (AB)nA+ or negative cluster ions (AB)nB−, respectively. The surfaces of the IL layers deposited on Si(100) substrates were flat at an atomic level for positive and negative cluster ion irradiation. Moreover, the contact angles of the deposited layers were similar to that of the IL solvent. Thus, surface modification of Si(100) substrates was successfully demonstrated with BMIM-PF6 cluster ion beams.

A review on ion–ion plasmas created in weakly magnetized electronegative plasmas

Ion–Ion plasmas are electronegative plasmas where the electron density is several orders of magnitude lower than the negative ion density. These plasmas have been scarcely observed and investigated since the 1960s and are formed as a transient state of pulsed plasmas or in separate regions in magnetized plasmas. In this review we focus on the latter case of continuous formation of ion–ion plasmas created at the periphery of magnetized plasma columns or downstream localized magnetic barriers. We bring together and review experimental results already published elsewhere and complement them with new results to illustrate the physics important in ion–ion plasma formation and highlight in particular unanswered questions. We show that with a good design the density in the ion–ion region is dropping only by a factor of 2–3 from the initial plasma density. These plasmas can therefore be well suited for various ion source applications when both fluxes or beams of positive and negative ions are desired, and when electrons can cause harmful effects.

Experimental validation of the dual positive and negative ion beam acceleration in the plasma propulsion with electronegative gases thruster

The PEGASES (Plasma Propulsion with Electronegative Gases) thruster is a gridded ion thruster, where both positive and negative ions are accelerated to generate thrust. In this way, additional downstream neutralization by electrons is redundant. To achieve this, the thruster accelerates alternately positive and negative ions from an ion-ion plasma where the electron density is three orders of magnitude lower than the ion densities. This paper presents a first experimental study of the alternate acceleration in PEGASES, where SF6 is used as the working gas. Various electrostatic probes are used to investigate the source plasma potential and the energy, composition, and current of the extracted beams. We show here that the plasma potential control in such system is key parameter defining success of ion extraction and is sensitive to both parasitic electron current paths in the source region and deposition of sulphur containing dielectric films on the grids. In addition, large oscillations in the ion-ion plasma potential are found in the negative ion extraction phase. The oscillation occurs when the primary plasma approaches the grounded parts of the main core via sub-millimetres technological inputs. By controlling and suppressing the various undesired effects, we achieve perfect ion-ion plasma potential control with stable oscillation-free operation in the range of the available acceleration voltages (±350 V). The measured positive and negative ion currents in the beam are about 10 mA for each component at RF power of 100 W and non-optimized extraction system. Two different energy analyzers with and without magnetic electron suppression system are used to measure and compare the negative and positive ion and electron fluxes formed by the thruster. It is found that at alternate ion-ion extraction the positive and negative ion energy peaks are similar in areas and symmetrical in position with +/− ion energy corresponding to the amplitude of the applied acceleration voltage.

Plasma characteristics of single- and dual-electrode ion source systems utilized in low-energy ion extraction

Discharge characteristics in the upstream as well as in the downstream regions of a 50-eV positive ion beam were measured along the beam axis. Single- and dual-electrode configurations made of 0.1-mm diameter tungsten wires were tested. By varying the upstream discharge parameters, the shape of the sheath edge around the extractors, which can either be "planar" or "cylindrical," can be controlled. The sheath eventually affected the simultaneous extraction of ions and neutralizing electrons. The dual-electrode configuration at the lower discharge current, revealed a homogeneous discharge downstream. At this condition, the edge of the sheath can be inferred to be "planar" which allowed the uniform extraction and propagation of low-energy ions at longer distances. The dual-electrode configuration was capable of transmitting low-energy ions up to 70 mm downstream.

Hysteresis effects in the formation of a neutralizing beam plasma at low ion energy

In this paper, the PEGASES II thruster prototype is used as an ion source generating low-energy positive Ar ion beam, extracted without an external neutralizer. The ions are extracted and accelerated from the source using a two-grid system. The extracted positive ion beam current is measured on a large beam target that can be translated along the acceleration axis. The ion beam current shows a stepwise transition from a low-current to a high-current extraction regime with hysteresis. The hysteresis region depends strongly upon the beam target position. Langmuir probe measurements in the plume show high plasma potentials and low plasma densities in the low-current mode, while the plasma potential drops and the density increases in the high-current mode. The ion energy distribution functions of the beam are measured for different regimes of ion extraction. The ion beam extracted in the high-current mode is indicated by the presence of an additional low-energy peak corresponding to ions from an ion-beam plasma created in the downstream chamber, as well as 10–20 times higher intensity of the primary ion beam peak. The hysteresis behavior is explained by the formation of a downstream neutralizing beam plasma, that depends on the target position and pressure in agreement with a Paschen-like breakdown by secondary electrons. The obtained results are of high relevance for further development of the PEGASES thruster, as well as for improving existing neutralizer-free concepts of the broad-beam ion sources.

Ion trajectory control by computer output through isolation amplifier circuit

AbstractControlling voltages by a computer has many advantages in the field of ion optics as well as accelerator and nuclear physics. Ion trajectory control needs many power supplies and fine voltage adjustment. Moreover, it is necessary to control the negative voltage for the extraction of a positive ion beam. However, the negative voltage of a general power supply cannot be controlled by its external control terminal because the negative port of the external control terminal and the negative output are internally connected in a general power supply. We construct a system to output a negative voltage using the external control terminal of a general power supply and an isolation amplifier that isolates the power supply and the output of the computer. The system requires no special power supplies or devices connecting the power supply and the computer. Moreover, the system can sweep and optimize the voltages to maximize an object function. A variety of output voltages can be controlled and optimized by this system. The system can optimize voltages one by one or multiple voltages simultaneously. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Irradiation of ionic liquid ion beams on silicon and glass substrates

Irradiation of an ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6) ion beam on borosilicate glass and single crystalline Si(100) surface was demonstrated by using an ionic liquid ion source we developed. Surface smoothing on the glass substrates was produced by the irradiations at an acceleration voltage of 4kV with both positive and negative ion beams, which include cation–anion pairs attached to a single ion of either polarity. Water contact angle measurements and X-ray photoelectron spectroscopy indicated that the surface smoothing was probably caused by surface modification involving nano-ordered chemical etching by Si–F reaction, implantation and deposition of P, N and C.

1932, a watershed year in nuclear physics

The consequences, for good and ill, of that annus mirabilis of discovery and invention are still very much with us.

Production and irradiation of ionic liquid cluster ions

We have developed a field-emission-type of cluster ion source using ionic liquids such as 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6). The current obtained was stable by placing a porous cap around the emitter. Time-of-flight (TOF) measurement showed that the peak mass number was approximately 5000 for positive and negative BMIM-PF6 ion beams. This indicated that BMIM-PF6 clusters with a size of a few tens of molecules were produced. With regard to the surface modification by BMIM-PF6 ion beams, positive and negative cluster ion beams were used to irradiate Si(100) and glass substrates. Scanning electron microscope (SEM) and atomic force microscope (AFM) observations showed that the surface roughness of substrates increased. Furthermore, X-ray photoelectron spectroscopy (XPS) measurement showed that the composition ratio of layers deposited by positive or negative cluster ion beams was similar to that of BMIM-PF6 solvent.

Normal-incidence Electron Gun alignment method for negative ion analysis on insulators by magnetic sector SIMS

On Cameca magnetic sector SIMS (Secondary Ion Mass Spectrometer) instruments, detection of negative secondary ions during analysis of insulating materials represents one of the more challenging uses of the instrument. This is because the highest sensitivity is achieved using a positive Cesium primary ion beam to sputter a sample held at a negative potential. The combination of positive charge from the primary beam and the acceleration of negative ions from the sample surface results in the build-up of positive charge in the sputtered area. The Normal-incidence Electron Gun (NEG) is used to deliver electrons to neutralize the positive charge build-up. At typical conditions, the electron beam diameter is rather small (∼150μm), so it is critical to align the NEG to overlay the analysis area as closely as possible. A new method has been developed to utilize cathodoluminescence of gallium nitride (GaN) to visually align the electron gun. This approach is shown to result in reproducible analyses of insulating phases, including depth profiling of oxide on semiconductor materials, bulk analyses for hydrogen, and oxygen isotope ratio microanalyses.

Characteristics of ion-acoustic solitary wave in a laboratory dusty plasma under the influence of ion-beam

We study the influence of ion beam and charged dust impurity on the propagation of dust ion-acoustic solitary wave in an unmagnetized plasma consisting of Boltzmann distributed electrons, positive ions, positive ion beam, and negatively charged immobile dusts in a double plasma device. On interacting with an ion beam, the solitary wave is bifurcated into a compressive fast and a rarefactive slow beam mode, and appears along with the primary wave. However, there exists a critical velocity of the beam beyond which the amplitude of the fast solitary wave starts diminishing and rarefactive slow beam mode propagates with growing amplitude. Whereas, the presence of charged dust impurity in the plasma reduces this critical beam velocity and a substantial modification in the phase velocity of the slow beam mode is observed with increasing dust density. Furthermore, the nonlinear wave velocity (Mach number) as well as the width of the compressive solitons are measured for different beam velocity and dust density, and are compared with those obtained from the K-dV equation. The experimental results are found in a well agreement with the theoretical predictions.

Effect of ion temperature on small-amplitude ion acoustic solitons in a magnetized ion-beam plasma in presence of electron inertia

Existence of both compressive and rarefactive solitons are found to exists in a magnetized plasma model consisting of ions, electrons and positive ion beams using the Korteweg-de Vries (KdV) equation. Both fast and slow modes are found to exist due to the presence of ion temperature in the plasma. Moreover, the amplitude of the soliton decreases with an increase in temperature for Q′ (\(= \frac{m_{b}}{m_{i}}\), beam-ion mass to warm-ion mass ratio) >2 and the amplitude becomes maximum when the wave propagates parallel with the direction of the magnetic field. The investigation further revealed that though both compressive and rarefactive solitons exist for slow mode, only compressive soliton exist for the fast mode.

Molecular and negative ion production by a standard electron cyclotron resonance ion source

Molecular and negative ion beams, usually produced in special ion sources, play an increasingly important role in fundamental and applied atomic physics. The ATOMKI-ECRIS is a standard ECR ion source, designed to provide highly charged ion (HCI) plasmas and beams. In the present work, H(-), O(-), OH(-), O(2)(-), C(-), C(60)(-) negative ions and H(2)(+), H(3)(+), OH(+), H(2)O(+), H(3)O(+), O(2)(+) positive molecular ions were generated in this HCI-ECRIS. Without any major modification in the source and without any commonly applied tricks (such as usage of cesium or magnetic filter), negative ion beams of several μA and positive molecular ion beams in the mA range were successfully obtained.

Factors enhancing production, extraction and focusing of positive ion beams

In this work, historical review about different kinds of ion sources and their applications are reviewed and discussed. Principle of plasma generation and ion extraction are discussed and investigated. In all types of ion sources, ions are produced by various types of gas discharge including electron collisions with gas particles. The general parameters are a source of electrons, a small region of relatively high gas pressure, an electric field to accelerate the electrons in order to produce an intense gas discharge (plasma) with a relatively high electron and ions density and some mechanism for extracting a collimated parallel high current ion beam. Types of gas discharges and different ionization processes are described. Optimum extraction conditions are reached whenever the plasma meniscus has an optimum curvature for a given current density. Also, different patterns of emittance diagrams for a typical illustration pictures with the aid of SIMION computer program are given. Indeed, theory of ion focusing is given and some examples on electrostatic focusing systems as two and three cylinder lens systems are given. These studies clearly demonstrate the importance of being able to produce, focus and adjust the extraction region in order to ensure high quality, minimum divergence (highly transportable) ion beams. The ion source is evaluated by; the large ion current extracted from it, the large percentage of ions in the beam, the higher degree of ionization inside the atom, the small gas consumptions, and the degree of divergence of the extracted ions must be small.

Effect of multi-ions on electromagnetic ion-cyclotron waves with a hot plasma around the polar cusp

Electromagnetic ion cyclotron (EMIC) instabilities with an isotropic ion beam and general loss-cone distribution of hot core plasmas are discussed. The growth rate of the wave, perpendicular heating of ions, parallel resonant energy and marginal instability of the EMIC waves in homogeneous plasmas are obtained using the dispersion relation for hot plasmas consisting of H+, He+,O+ ions and electrons. The wave is assumed to propagate parallel to the static magnetic field. The whole plasma is considered to consist of resonant and non-resonant particles permeated by the isotropic ion beam. It is assumed that the resonant particles and the ion beam participate in energy exchange with the wave, whereas the non-resonant particles support the oscillatory motion of the wave. We determined the variation in energies and growth rate in hot plasmas by the energy conservation method with a general loss-cone distribution function. We also discuss the effect of positive and negative ion beam velocity on the growth rate of the wave. The thermal anisotropy of the ions of the core plasma acts as a source of free energy for EMIC waves and enhances the growth rate. Heating of ions perpendicular to the magnetic field is discussed along with EMIC wave emission in the polar cusp region.